Soil organic carbon (SOC) plays an essential role in carbon sequestrationclimate change mitigation in forest ecosystems. While experimental studies have shown that plant diversity usually increases SOC, it remains unclear whether this positive relationship holds in natural ecosystems across varying climatic conditions.

Using a global dataset of 15 largelong-term monitored natural forest sites spanning a wide latitudinal range, we assess the relationship between tree diversitySOC withinacross sites in temperate, subtropical,tropical regions. 

We found an overall positive relationship between tree taxonomic diversitySOC. The relationships between tree taxonomicfunctional diversitySOC became stronger under coldermore arid conditions. Additionally, tree functional composition was linked to SOC only within a subset of sites in more arid climates. 

These findings suggest that warmermore humid conditions increase decomposition, offsetting diversity-driven carbon inputs, while coldermore arid conditions enhance SOC through low decompositionincreased inputs through abiotic facilitationbiotic interactions in high-diversity communities. Our findings indicate that conserving plant diversity is critical for enhancing carbon sequestrationmitigating the effects of climatic conditions, particularly in cold climatesregions facing an increase in arid conditions.